Induction motor



SWL'Y 1, 5925.

M.ARENDT INDUCTION MOTGR Filed Aug. l5 1.

FBO

Patented Sept. 1, 1925.

UNITED STATES MORTON ABENDT, OF NEW YO'RK, N. Y.

INDUCTION MOTOR.

Application filed August 15, 1921. Serial No. 492,227.

To all whom t may concern.'

Be it known that I, MonToN ARENDT, a citizen of the United States, residing at New York, in the county of New York, State of New York, have invented certain neuT and useful Improvements in Induction Motors; and I do hereby declare the following to be a full, clear, and exact description of the invention, such as will enable others skilled in the art to which it appertains to make and use the same. l l

This invention relates to induction-niotors.

It is common practice to provide single phase induction motors with an auxiliary or starting winning in parallel with the working winding on either the stator or the rotor. These winding are ,electrically displaced, so that the motor'operates as a split phase machine upon starting, the diiierence in phase between the currents in the two windings resulting in a torque sufficient to initiate rotation. When l moderate speed has been attained, it is no longer either necessary or desirable to operate as a split phase machine, and some means must be employed to throw the starting winding out. This may be done by hand, but is usually done by `means of a centrifugal switchl on the rotor designed to throw out at a predetermined speed. `These switches, as commonly designed, are opento certain objections. `As the speed approaches thepoint of throw out, the switch chatters, that is, makes and breaks in rapid succession before the final break, and this is true no matter how strong a spring be used to rcounteract the centrifugal force. This results in excessive sparking with consequent impairment of the contacta serious disadvantage where the break is made at thefpoint of contact during lthe split phase operation.

Again; these switches throw in at thesame speed at which they throw out. a disadvantage.` As the st'artingwindi'ngis light, it is likely to burn out if used when the motor is loaded. It is, therefore,xdesirable that the speed be allowed to` slacken, due to overloading,` belowthe throw out speed, without throwing the starting wind ing in;l and this then is an object of the present invention.

In the attainment of this obj ect the swinging Vcontact member of the. switchl is so mounted that it makes contactkwith a notch displaced from its plane of movement, so that in throwing out, the centrifugal force This is i must vovercome not only the force of the Ordinary spring, but also the friction between the contact member and the side walls of itsnotches. In throwing in, the spring only is effective. This means that the motor can be overloaded below the speed of cut-out without throwing the starting winding in.

I mount the spring so that it does not weaken as the switch arm is thrown out. This obviates the usual tendency for the spring to snap the switch into contact as the speed of the motor diminishes. In practice, I have found a leaf spring well adapted for the purpose.

Another phase of the invention relates to the concentric collector rings, commonly employed on induction ymotors. These rings, according to the general practice, are mounted upon a disc of insulating libre and the whole mounted upon the shaft of the rotor. There is no space between the inner ring and the collar which mounts both rings upon lthe rotor shaft, and the fibre disc being continuous there is no open space between the rings themselves, although these rings are, of course, separated from each other. As a result of this construction there is no possibility of ventilation through the rings, and in small motors in which there is little space between the outer ring and the motor housing, this is a serious objection and results in overheating the motor. Moreover, the fibre disc forms. the bottom of an annular groove between the two rings in which carbon dust from the brushes collects, when the rings are horizontal, short circuits the motor, and burns the rings. This is particularly likely to happen wherethe working winding is connected to the rings so that the potentialI difference between the rings is a maxi* mum. It is accordingly a further object of this invention to mount these rings so that ventilation through them is possible and so .that carbon dust cannot collect to l cause trouble.

tails. .ln these drawings, Fig. 1 is a vertical section through the housing showing the rotor, collector rings, brushes and switch in elevation. Figure 2 is a diagrammatic view ot the collector rings and switch taken in general along` line 2 2 of Figure 1 and showing the wiring` system. In order. that the operation ot the switch may be more clearly shown the parts in Figs. 1 and 2 do not exactly correspond as will be apparent from a detailed study oit them. Figure 3 is a detailed view et centrifugal switch contacts showing the relation of the swinging member or blade to its notch.

The induction motor shown in Fig. l comprises a housing 1, a stator 2, a vertically mounted rotor 3 mounted upon a shatt 4, concentric collector rings 5 and 6, and spring pressed carbon brushes 7 and 8 contacting with rings and 6, respectively. The collector rings are mounted upon a spectacle shaped support 9 comprising a central collar 11 held upon the shaft, 4 by means ot a set screw 12. The eyes 13 ot the spectacle extend diametrically from each other on opposite sides ot the collar 11. and are tilled with hard rubber or other insulating material 14 which extends beyond their inner faces and constitutes an insulating support tor the collector rings. The inner ring- 6 is spaced 'from the collar 11 by an annular space .l5 and the two rings are spaced from each other by another annular space 16, these spaces extending completely through the rings and affording a passageway tor air. r

The rotor is provided with a working winding 17 and an electrically displaced starting winding 18 in parallel with the working winding, the two being so arranged that when the current is tirstf turned on a torque results suiiicient to start rotation. ln creer to throw out the starting winding when sutlieient speed has been attained a centrifugal switch 19 is employed. This switch comprises a stationary arm 23 mounted upon the insulation l-t ot one oi. the spectacle eyes 13. Pivoted at 24 about one end ot this arm 23 is swinging member or contact blade 25 constantly urged into contact with a pin 26 by means ot' a leaf spring 27. Thel contact end of the blade 25 is provided with a bevelled edge 28 provided with an arcuate groove which is designed to fit within a notch 29 in the pin 26. The blade normally swings in a plane slightly offset from the plane ot the notch 29 as clearly shown in Fig. 3, but is pivoted at, 24 with a certain looseness so that the pressure of the spring 27 holds it normally seated within the notch 29. When, under the action of centrifugal torce this blade 25 tends to move outwardly it climbs along the outer wall ot the notch 29 making frictional contact wit-l1 it. The result is that the centrifugal torce necessary to unseat it must not only counteract the force of the spring 27, but also the added rictional resistance of the notch 29 against the edge 28 of the blade. rllhis trictional drag also tends to overcome chattering for when the blade has cleared the notch the rictional resistance .is removed and the blade can Atly outwardly. In any event the blade does not chatter when seated so that the contact points during the split phase operation are not injured. A pin 31 on the outer ring serves to limit the outward movement of the swinging member.

The leaf spring 27 is bowed out as the blade 25 swings away trom pin 26, its rec sistance increasing with the outward movement of the blade. Upon the return movement its torce decreases as the blade approaches the pin and thus there is little tendency for it to snap quickly into contact. This further enables the motor to slow down below throw-out speed before the starting winding is thrown in. Moreover by employing a leaf spring instead of a coil there is no danger of sagging and short circuiting through contact oft the spring with the metal frame -13 ot the spectacle support.

In order that the general operation oit the system may be clearly comprehended attention is now called to the wiring diagram shown in Fig. 2. An alternating current generator is indicated at 'from which leads extend to the brushes 7 and 8. One terminus ot' both the working and starting windings is connected to outer ring 5 through contact 21. The other terminus ot the working winding is connected to the inner ring 6 through contact A2,2, and the other terminus of the starting winding is connected to the inner ring: 6, through the arm 23, blade 25 and pin 26 of the centrifugal switch 179. then current is turned on both windings being in parallel are energized as will be clear from the study of Fig. 2. The resulting torque starts the motor. As the speed accelerates a certain predetermined point is reached where it is desirable to throw out the starting winding. At this point the blade of the switch is thrown away from pin 26 and rests upon pin 31. lhen in this position the starting winding is disconnected from the inner ring and no current can pass through it. The spring 27 is so adjusted that on a two pole cycle machine, the arn'iature makes about 2600 revolutions per minute before contact between the pin 26 and the switch arm 25 is broken by centrifugal force.v After the break the motor continues to operate as a true single phase induction motor at substantially synchronous speed.

Should the speed of the motor be decreased, due to over-load, the switch 19 will not immediately operate to throw in the starting winding because the only torce tendllt) lli

ing to move the arm 25 into contact with pin 26 is the force of spring 27, whereas in throwing the switch out centrifugal force must overcome not only the force of this spring, but also the frictional drag of the blade along the wall of the notch 29. Contacts 2l and 22 are made in the form of fan blades as will be clear from a study of Figs. l and 2. rhe result is that they perform two functions. They not only serve as contacts for the winding but they serve to induce a current of air through the annular spaces between the rings and thus cool the motor.

From the foregoing description it will be clear that the objects of the invention have been attained. By eliminating the common libre disc upon which the collar rings have heretofore been placed and employing a socalled spectacle support, it has been possible to space the rings apart and from the rotor shaft. This structure performs two functions. t not only permits of ventilation to cool the motor, but when the rings are horizontal it prevents a collection of carbon duct from the brushes within the annular space between the rings. As this dustu is commonly the cause of short circuiting and biu'ning, this is a highly advantageous result, particularly in the present construction where the potential difference between the rings is relatively high. By offsetting the swinging member of the centrifugal switch from the plane of its contact notch, a siniple method has been devised for making the speed of the break slightly greater than that of the malte so that the motor may operate at overload without throwing in the starting winding.

claim:

l. In an induction motor, the combination of a support for collector .rings mounted upon the rotor shaft, concentric collector rings mounted upon said support with annular spaces between the inner ring and the shaft, and between the two rings, said spaces permitting the passage of air, a winding on the rotor, and contacts between the winding and the rings shaped like fan blades to induce a current of air through the rings.

2. .ln an induction motor, the combination of a spectacle shaped support for collector rings mounted upon the rotor shaft, concentric collector rings mounted upon said support and insulated therefrom with annular spaces between the rings, said spaces permitting the passage of air, a working winding on the rotor, one end of which is connected to one ring and the other to the other ring, a swinging switch member mounted on one of the spectacle eyes, a Contact pin on the inner ring, a starting winding on the rotor one end of which is connected to the outer ring and the other end to the swinging switch, and .means for holding the swinging switch in contact with the cont t pin to complete the circuit to the starting winding, and designed to be overcome by centrifugal force to throw out the starting winding when a predetermined speed has been attained.

In testimony whereof l aflix my signature.

MORTON ARENDT. 

